The invention relates to photographing data indicator for a single lens reflex camera, and more particularly, to an indicator which includes a liquid crystal display panel to display photographing data such as shutter speed, diaphragm aperture or the like within a viewfinder of the camera.
The use of a liquid crystal display panel to display photographing data such as shutter speed or diaphragm aperture within the viewfinder of a single lens reflex camera is already well known. The conventional arrangement comprises a liquid crystal display panel which is disposed laterally adjacent a scale on a front surface on which graduations for photographing data such as shutter speed are inscribed, and an exciting voltage is applied to energize a particular drive electrode which is aligned with a given point on the scale so that a corresponding area of the panel may be rendered opaque. However, this technique is disadvantageous in that it requires an increased lateral space where a number of photographing data are to be displayed. By way of exaple, if it is desired to display both the proper value of shutter speed which is derived from a photometric circuit of the camera and the actual value of shutter speed which is preset on a shutter speed presetting dial of the camera (so as to provide a display which simulates a display produced by an exposure controller of the type in which the pointer of an exposure meter moves toward a light indicative of a proper exposure level as the dial is moved), or where it is desired to display both the values of shutter speed and diaphragm aperture, two or more rows of liquid crystal display panels must be laterally juxtaposed with the photographing data scale. In order to maintain these rows of display panels within the sight of a viewer together with the picture plane of the finder, it is necessary that the viewfinder be provided with an increased field of view. This requires that the lateral dimension of the pentaprism be increased, which also necessitates that the vertical dimension of the prism be increased in addition to the lateral dimension due to design considerations. This results in an increased size of the pentaprism and an increased weight and volume of the camera, causing an increased cost of the camera.
To overcome this difficulty, a photographing data indicator for single lens reflex camera (see Japanese Utility Model Publication No. 4,817/1980) has been proposed which permits more than one piece of data to be concurrently displayed without increasing the lateral dimension of the display, by disposing a pair of liquid crystal display panels in superimposition with each other below a transparent glass pane on which a data scale is inscribed, utilizing the characteristic of a liquid crystal display panel that a light transmittivity equal to or greater than 90% is available when it is not energized. Such a display unit 1 is illustrated in FIG. 1, and comprises a bank of liquid crystals 2 which are used to provide a display of a proper value of shutter speed and which are enclosed in a pair of transparent glass panes 4, and another bank of liquid crystals 3 for providing a display of a manually preset value of shutter speed and which are also enclosed in a pair of transparent glass panes 5, both the glass panes being disposed in overlying relationship with each other. A shutter speed scale 6 is formed or inscribed on the surface of the topmost glass pane 4. As shown in FIG. 2, the display unit 1 is interposed between a focusing glass 7 and a pentaprism 8 forming part of the finder optics of a single lens reflex camera, toward one lateral edge thereof. In FIG. 2, numeral 9 represents a stationary member which supports the focusing glass 7, and 10 represents a movable reflecting mirror.
In the use of the display unit 1, FIG. 3 illustrates that an output from a photometric circuit of the camera energizes one of the liquid crystals in the bank 2 which corresponds to a point on the scale 6 representing a proper value of shutter speed. Simultaneously, one of the liquid crystals in the bank 3 which corresponds to a point on the scale 6 corresponding to a value of shutter speed which is manually preset on the shutter speed dial of the camera is energized. As an example, the proper value of shutter speed is shown as 1/500 second while the manual preset value is equal to 1/125 second. In this manner, both the values are simultaneously displayed.
However, the described indicator 1 requires that the spacing between the focusing glass and the pentaprism be increased in order to allow the indicator to be disposed therebetween inasmuch as the pair of laminated liquid crystal display panels results in an increased thickness. The increased spacing between the focusing glass and the pentaprism results in a relatively high elevation where the pentaprism is located. This increases the height of the camera, causing an increased size of the camera, a reduced finder magnification and a reduced accuracy of the focusing operation.